I would never ever recommend selling replicas of licensed and trade marked work as it can have MAJOR legal repercussions. For example, Square Enix has recently become VERY strict about the making and selling of replica swords/items from any of their games. I can only imagine how Microsoft would get if this became a trend.
However, besides all that.
I made myself a Halo 3 AR a while back using the pepakura method. It wasn't easy, but it was fun and it turned out great. Pepakura, while not easy, isn't by any means hard. It is just very time consuming.
I don't know what you have learned about pepakura, but the first thing you need are the programs.
Pepakura viewer and pepakura designer (I would suggest getting both, after all, they are just resources, and having as many as possible is a good idea)
Once you have the programs, you need the pep file for the 'unfolded' item you want to make. Make sure to follow any special instructions, for example, sizing the pieces to fit standard 8.5x11 paper. Once that's done, print the files and begin to cut out the shapes. After that, fold the lines according to the peaks and valleys and then hot glue it all together. Once that's done, you are ready for the next steps. But, take it slow.
I hope anything I have provided helps, I hope the amount of effort doesn't make you think twice about working towards something awesome!